1. Field of the Invention
This invention relates to methods of treating tumors and bacterial or viral pathogens, and more particularly to methods of treating tumors and bacterial or viral pathogens using isoaspartyl-modified proteins to enhance immune response. The invention also relates to vaccines and antibodies used in these treatments.
2. Brief Description of the Related Art
The immune system has evolved to be tolerant of self-proteins by the deletion of autoreactive cells in the thymus or bone marrow and by the establishment of B and T lymphocyte anergy in the peripheral circulation (Billingham, R. E. et al., Nature 172:603-606, 1956; Schlid, H. et al., Science 247:587-589, 1990). These mechanisms are based on the presentation of a vast array of self-peptides to the lymphoid repertoire. Despite the efforts to instruct the immune system to ignore self-tissues, the appearance of various autoimmune diseases demonstrates that tolerance to self-antigens is not perfect. Flaws in the development of immune tolerance can be revealed by the immunization of animal models with a variety of self-peptides leading to B and T cell autoimmunity as well as autoimmune-mediated pathology (Lehman, P. V. et al., Nature 358:155-157, 1992; Mamula, M. J., J. Exp. Med. 177:567-571, 1993; Bockenstedt, L. K., et al., J. Immunol. 154:3516-3524, 1995).
How tolerance is broken in the initiation of autoimmunity is not completely understood. The immunization of mice with a single self-peptide, the amino-terminal 11 amino acids of myelin basic protein (MBP) in complete Freund's adjuvant can elicit pathology resembling that of human multiple sclerosis (Lehman, P. V. et al., Nature 358:155-157, 1992). The induction of disease requires a post-translationally acetylated form of MBP peptide 1-11. While this disease can be elicited with a single self-peptide or event with T cells of a single specificity, the autoimmune response diversifies to many sites on the MBP over the course of the disease. T cell responses originate with the dominant single self peptide but rapidly evolve to include other cryptic peptide epitopes within MBP. Similar observations of determinant spreading have been made in murine models of diabetes and systemic lupus erythematosus (SLE), two diseases arising spontaneously in susceptible strains of mice (Kaufman, D. L. et al., Nature 366:69-72, 1993; Bockenstedt, L. K., et al., J. Immunol. 154:3516-3524, 1995); Fatenejad, S. et al., J. Immunol. 152:5523-5531, 1994).
Antinuclear antibodies specific for double-stranded DNA and the U1/Sm ribonucleoprotein particle (snRNP) are diagnostic markers of SLE. The snRNP particle is an RNA-protein complex essential for the splicing of pre-mRNA (Wassarman, D. A. et al., Science 257:1918-1925, 1992). Proteins designated B, B′, and D comprise the target proteins of anti-Sm autoantibodies in SLE patients. It is not known how high affinity autoantibodies and autoreactive T cells arise to these intracellular proteins the mature phenotype of autoantibodies found in diseases such as SLE indicates that autoimmunity is driven by helper T lymphocytes and a source of antigen (Steinberg, A. D., et al., J. Immunol. 125:871-873, 1980; Jevnikar, A. M. et al., J. Exp. Med. 179:1137-1143, 1988; Tan, E. M. Adv. Immunol. 44:93-151, 1989).
While it is clear that autoimmunity can spread to several sites on an autoantigens over the course of experimentally induced disease models, the initiating antigenic peptide in naturally arising disease is unknown. A hypothesis of molecular mimicry implies that foreign pathogens that share amino acid sequences with self-peptides can break immunologic tolerance in the induction of autoimmunity. However, no pathogen has been unambiguously linked with the induction of any human autoimmune syndrome. Alternatively, the present inventors have initiated studies to consider forms of self-antigens that can be viewed as foreign by the immune system. The immune system does not respond to immunization with selected peptides from self-proteins. However, when the same self-peptides are converted to the isoaspartyl isoform, vigorous autoimmune responses develop upon immunization. After initiation by the isoaspartyl peptide isoforms, autoimmunity is amplified to other peptides on the autoantigen.
Isoaspartyl peptides arise spontaneously under physiologic conditions and are particularly elevated in cells undergoing stress and in aging cells. The presence of isoaspartyl peptides have been observed as a major component of the amyloid-containing brain plaques of patients with Alzheimer's disease. With relevance to immune responses, it is possible that tolerance to these forms of self proteins fails to occur early in lymphocyte development. Based on the enhanced immunity to some isoaspartyl self-peptides, it is possible that an accumulation of these aberrant peptides may be an early stimulus for autoimmune responses.
The present inventors have previously shown that isoaspartyl modifications of “self” proteins (e.g., proteins recognized by a cell as it's own) can result in autoimmunity. In these studies, it was shown that autoimmunity could be generated to isoaspartyl-modified self proteins, such as cytochrome c, while the identical unmodified protein would elicit no response from the immune system (Mamula, M. J. et al., J. Biol. Chem. 274:22321-22327, 1999). Applications of this phenomenon, however, were not disclosed.
Tumor antigens are considered a form of self protein to which little immune responses are generally elicited. This lack of immunity allows the tumor cells to proliferate and spread without the interference of immune responses that may attack and destroy the tumor cell. In a similar manner, many proteins on the surfaces of viral particles (such as gp proteins on the surface of HIV) are only weakly antigenic in eliciting responses of the immune system. These properties of viral and bacterial proteins allow for their survival in the host.
What is needed in the art is a method of identifying the weakly antigenic proteins found on tumors, bacteria and viruses, and a vaccine and antibody that can select and eliminate these weakly antigenic species. The present invention is believed to be an answer to that need.